1. Field of the Invention
The invention relates to a delay-locked loop for data recovery, and more particularly, for recovering the Manchester coded digital data having two kinds of fixed length of "1" and "0" to its original data.
2. Description of the Related Art
FIG. 1 schematically illustrates coding of a Manchester code, while FIG. 2 gives a sample of the coded result. For Manchester code, there are only two kinds of fixed lengths for continuous "1" and "0". For example, the two lengths of Ether Net application having a transferring speed of 10 Mbps are 50 and 100 ns.
The disadvantages when using the typical phase-locked loop to recover the clock/data are that: (1) since the signal contains different length of "0" and "1" which do not have a fixed period, the phase-locked loop can not be stabilized easily; (2) the phase-locked loop adjusts the frequency of recovering clock to synchronize the signals, which also causes the accumulation of phase errors from one period to the next period; and (3) the loop filter of a phase-locked loop is a RC circuit which results in the resistor and capacitor often occupying most of the area during the manufacture of a semiconductor device. In addition, because each port requires a respective set of phase-locked loop during a multiport application, the increase of area is directly proportional to the increase of number of ports.